# Greetings from The On-Line Encyclopedia of Integer Sequences! http://oeis.org/ Search: id:a281407 Showing 1-1 of 1 %I A281407 #14 Jun 08 2024 15:41:23 %S A281407 0,2,4,9,14,20,28,33,156,285,302,1121,1300,2540,3873,4706,5297,7292, %T A281407 11086,15928,16203,17267,17793,19326,32009,67659 %N A281407 Numbers k such that (292*10^k - 1)/3 is prime. %C A281407 Numbers k such that the digits 97 followed by k occurrences of the digit 3 is prime (see Example section). %C A281407 a(27) > 2*10^5. %H A281407 Makoto Kamada, Factorization of near-repdigit-related numbers. %H A281407 Makoto Kamada, Search for 973w3. %e A281407 2 is in this sequence because (292*10^2 - 1)/3 = 9733 is prime. %e A281407 Initial terms and associated primes: %e A281407 a(1) = 0, 97; %e A281407 a(2) = 2, 9733; %e A281407 a(3) = 4, 973333; %e A281407 a(4) = 9, 97333333333; %e A281407 a(5) = 14, 9733333333333333; etc. %t A281407 Select[Range[0, 100000], PrimeQ[(292*10^# - 1)/3] &] %o A281407 (PARI) isok(n) = isprime((292*10^n - 1)/3); \\ _Michel Marcus_, Jan 21 2017 %Y A281407 Cf. A056654, A268448, A269303, A270339, A270613, A270831, A270890, A270929, A271269. %K A281407 nonn,more,hard %O A281407 1,2 %A A281407 _Robert Price_, Jan 21 2017 # Content is available under The OEIS End-User License Agreement: http://oeis.org/LICENSE